He's a good writer. I haven't read all of them yet -- I'm about halfway through the first one and was quite impressed, but as with most books that are reasonably challenging, I keep getting distracted, since it takes longer than just a few hours to read.

Edit: One thing in it that I keep thinking about is how he took the four classical Greek personality types and combined them with another set of classical personality types that I forget and came up with modern psychological types. Very interesting. I like stuff like that, and that was just a tangent (as far as I could tell from that point -- it might turn out to be very relevant, so don't spoil it ).